THE
FOUR C's
OF
COLORED STONES

You're probably familiar with the four "C's" of diamonds,
but you may not have heard as much about the four "C's" of colored stones.
Colored stones include all stones except diamond, even though many other
gemstones can also be clear and transparent.

COLOR

You are first attracted to a gemstone by its color.
Color can been classified by:

HUE (red,green, bluish-green, etc.)

TONE (lightness or darkness)

SATURATION (intensity)

More about color

CLARITY

The second thing you see involves clarity. Clarity
refers to:

BLEMISHES (on the surface)

INCLUSIONS (internal characteristics or
irregularities within the stone)

Each stone is unique and its inclusions can be
used as "fingerprints" to identify it. Unlike the standard grading system
in place for diamonds, colored stones do not yet have a universally accepted
system.

More about clarity

CUT

Cut does not refer to the shape of a stone, but
to how well it is cut or its:

PROPORTIONS and FINISH

Colored stones are faceted into many different
shapes, including the round brilliant, oval, emerald step cut, heart, marquise
and pear. Whatever your preference, the importance of a well-cut stone
is obvious! You can spot a well-cut stone because it sparkles with life!
You don't want to see through the bottom of the stone! This is called a
"window" and most stones with windows do not have much brilliance.

Well cut

Too shallow

Too deep

More about cut

CARAT
WEIGHT

Colored gemstones are weighed in carats as are
diamonds. A one carat diamond is approximately 6.5 mm in diameter. Colored
stone weights will vary due to the differences in the angles used in cutting
and their specific gravity. Prices will vary greatly as well, just as they
do with diamonds.

More about carat weight

In looking at all these aspects,
you can begin to gain more awareness and
a greater appreciation of the beauty and wonder of the mineral kingdom!

ADDENDUM TO THE FOUR
C's

COLOR

GIA has developed a system that describes colors
very accurately, using 33 hues, tones from 1 to 6, and saturations from
0 to 10. In addition to the dominant bodycolor of the stone, there can
be additional colors, due to pleochroism (tanzanite), color-change (alexandrite),
color zoning (tourmaline) and for other reasons.

Return to Color

CLARITY

Because of the wide variety of colored stones, three
clarity types have been proposed for use with the GIA system. Type I stones
can generally be found to be almost inclusion-free (such as topaz). Type
II stones are usually included (such as garnet), and Type III stones are
almost always included (such as emerald). Each stone is compared with others
of its type, and is classified using eight categories from VVS (very small
inclusions) to Declasse (inclusions interfering with the light so much
that it is not transparent).

Return to Clarity

CUT

The sparkle is due to the stone's brilliance from
being cut at angles which allow the light entering the crown (top) of the
stone to bounce around in the stone, and return out through the crown,
rather than absorbing the light, or leaking it out through the pavilion
(bottom) or sides. Cut includes both proportions and finish. Good proportions
include a pleasing face-up outline, brilliance and profile. Finish includes
a smooth polish and symmetrical facets.

PROPORTIONS (relationships among crown,
girdle, pavilion):

a. From the top:
outline
length to width ratio
evenness
is there a window? b. From the side:
girdle thickness
depth of stone (2:1 to 3:1)
bulges?
symmetrical profile?

CARAT
WEIGHT

The price variations are due to several factors,
including the above mentioned color, clarity, cut and carat weight. In
general, the rarer the stone, the more valuable it is. Some stones are
readily available in larger sizes, so a 6 carat stone may be twice the
price of a 3 carat stone. Others, such as ruby or tanzanite, may be 10
or more times the price.

Return to Carat Weight

WATCH
OUT FOR WINDOWS!

EVALUATING
THE CUT OF A GEMSTONE

Many people ask for advice on how to choose a gemstone
for jewelry. We often hear about the 4 C's of Diamonds or Colored Stones:
Color, Clarity, Cut and Carat weight. This discussion will focus on cut
(make), not referring to the shape of the stone, but to how well it is
cut.

G.I.A., one
of the primary educational and testing organizations in the world, separates
cut into two parts: proportions and finish. Proportions refers to the relationships
among the crown (top), girdle (middle) and pavilion (bottom). First, look
down at the top of the stone to determine if the outline is pleasing. Check
the length to width ratio, evenness of each side, etc. Do you see straight
through the top of the stone to the surface underneath? If so, this "window"
is stealing much of the brilliance and color that a better-cut stone would
offer you. The window suggests that the pavilion angle is too shallow for
the gem material. Each gem material has a specific refractive index (RI),
indicating the angle at which the light bends as it enters the stone. If
the pavilion is cut using too low an angle, you will see right through
the bottom of the stone (not a pretty sight in most stones). You will get
the greatest brilliance in a gemstone if the light goes in through the
crown, bounces around in the stone, and then exits back through the crown.
This has been called "optical excitement". Is the table (the flat top)
about 1/2 to 2/3 of the width of the stone?

Next, look at the stone from the side. Is the
girdle thick enough to be set in a standard setting without being chipped
(not a knife-edge), but not too thick to prohibit it from being set easily?
Is the depth of the stone, as well as its proportions (crown height, girdle
thickness and pavilion depth) pleasing, or is it too deep or too shallow?
Generally the pavilion depth should be 2 to 3 times the height of the crown.
This means that the ratio of the pavilion to the crown should be 2:1 to
3:1. Do either the crown or pavilion bulge out excessively? Is the profile
symmetrical?

After checking the proportions, look at the finish.
Finish consists of polish, symmetry, and suitability of facets. A good
Polish includes (1) a faceted and polished girdle (many stones cut overseas
have rough, rounded girdles), and (2) no lines, scratches or pits which
detract from the overall appearance of the stone. Symmetry refers to the
balance and consistency of the design and the regularity of the facets.
Are the facets in each tier the same size and shape? Do they point up,
that is, do they meet at the points where they should? Are the facet junctions
sharp, or are they rounded and misshapen? Are the facets in alignment,
that is, do they meet accurately at the girdle from the crown and from
the pavilion? Facet survey checks the appropriateness of the number and
size of the facets for that stone. Are there too many tiny facets in a
small stone, or too few in a large stone?

If all this seems like too much to remember at
one time, there are several things you can begin to do. First, look at
a lot of stones at Gem Shows, jewelry stores and lapidary shops. Ask questions.
Start with some of the basics:

(1) check for a window, (2) check the girdle to
see if it's polished and faceted, and (3) look for sharp facet junctions.
And be sure to ENJOY THE BEAUTY OF GEMSTONES, a gift to you from the mineral
kingdom!